Method and device for controlling multipriority in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system and, more specifically, to a method and a device for controlling a backoff timer on the basis of multipriority in a wireless communication system. The method for controlling a backoff timer in a terminal in which multipriority is set, according to one embodiment of the present invention, comprises the steps of: transmitting, to a network node, a non access stratum (NAS) request message which is set to a first priority level and does not have an access point name (APN); receiving a reject message for the NAS request message from the network node; and starting a session management (SM) backoff timer on the basis of the rejection message, wherein while the SM backoff timer is operated, the terminal is permitted to transmit a new NAS request message which is not set to the first priority level.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2013/008877, filed on Oct. 4, 2013, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/709,987,filed on Oct. 5, 2012, all of which are hereby expressly incorporated byreference into the present application.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a control method and device based on multiplepriorities in a wireless communication system.

BACKGROUND ART

Machine type communication (MTC) refers to a communication schemebetween one or more machines and is also referred to asmachine-to-machine (M2M) communication. Here, a machine refers to anentity which does not require direct human operation or intervention.For example, a device including a mobile communication module, such as ameter or a vending machine, may include a user equipment such as asmartphone which is capable of automatically accessing a network withoutoperation/intervention of a user to perform communication. Variousexamples of such a machine are referred to as an MTC device or terminalin the present specification. That is, MTC refers to communicationperformed by one or more machines (that is, MTC devices) without humanoperation/intervention.

MTC may include communication (e.g., device-to-device (D2D)communication) between MTC devices and communication between an MTCdevice and an MTC application server. Examples of communication betweenan MTC device and an MTC application server include communicationbetween a vending machine and a server, communication between a point ofsale (POS) device and a server and an electric meter, and communicationbetween a gas meter or a water meter and a server. AN MTC-basedapplication may include security, transportation, healthcare, etc.

Meanwhile, if congestion or overload occurs in a network, congestioncontrol may be performed in a control plane. For example, networkcongestion control may be performed at a non-access stratum (NAS) levelwhich is an uppermost stratum in a control plane between a terminal anda network control node in a radio interface. In general, if a networkcongestion occurs, a network may configure a back-off timer forinhibiting a request for a network for a predetermined time with respectto a terminal.

According to operation of a currently defined wireless communicationsystem, priority may be configured per terminals, and only one of “(NASsignaling) low priority” for a terminal supporting MTC or “(NASsignaling) non-low priority” for a terminal supporting non-MTC.

Meanwhile, if network congestion or overload occurs, a back-off timer(BOT) may be used in order to distribute network load. Back-off timersmay be classified into a Mobility Management (MM) back-off timer and aSession Management (SM) back-off timer. MM back-off timer defines a timein which a terminal is prohibited from performing MM-related operationssuch as an attach request, SM back-off timer defines a time in which aterminal is prohibited from performing SM-related operations such as asession establishment/modify request related to an Access Point Name(APN).

DISCLOSURE OF THE INVENTION Technical Task

An object of the present invention devised to solve the problem lies ina new method for, at a UE configured for multipriority, performingoperation based on an SM backoff timer and priority when the SM backofftimer without an APN is running.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

Technical Solution

The object of the present invention can be achieved by providing amethod of controlling a backoff timer at a user equipment (UE)configured for multipriority including transmitting a non access stratum(NAS) request message without an access point name (APN), which is setto a first priority level, to a network node, receiving a reject messagefor the NAS request message from the network node, and initiating asession management (SM) backoff timer based on the reject message,wherein a new NAS request message, which is not set to the firstpriority level, is permitted to be transmitted by the UE while the SMbackoff timer is running.

In another aspect of the present invention, provided herein is a userequipment (UE) device for controlling a backoff timer if multipriorityis set including a transceiver module, and a processor, wherein theprocessor configured to transmit a non access stratum (NAS) requestmessage without an access point name (APN), which is set to a firstpriority level, to a network node using the transceiver module, toreceive a reject message for the NAS request message from the networknode using the transceiver module, and to initiate a session management(SM) backoff timer based on the reject message, and wherein a new NASrequest message, which is not set to the first priority level, ispermitted to be transmitted by the UE while the SM backoff timer isrunning.

The embodiments of the present invention have the following features.

A new NAS request message, which is set to the first priority level, maynot be permitted to be transmitted by the UE while the SM backoff timeris running.

The UE may not provide the APN during a procedure initiated bytransmitting the NAS request message.

The procedure initiated by transmitting the NAS request message may bean attach procedure.

The NAS request message without the APN may be an attach request messagewithout an APN.

The NAS request message without the APN may be an attach request messagetransmitted along with a packet data network (PDN) connectivity requestwithout an APN.

The reject message may include a value for the SM backoff timer.

The reject message may be received due to insufficient resources.

The UE configured for multipriority may be a UE configured for dualpriority.

The first priority level may correspond to the UE being configured forNAS signaling low priority.

The first priority level may correspond to a low priority indicator,which is set to the UE being configured for NAS signaling low priority.

The UE may be a machine type communication (MTC) device.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, it is possible to provide a newmethod for, at a UE configured for multipriority, performing operationbased on an SM backoff timer and priority when the SM backoff timerwithout an APN is running.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram showing the schematic architecture of an evolvedpacket core (EPC);

FIG. 2 is a diagram showing examples of an MTC communication model;

FIG. 3 is a diagram showing an exemplary model of an MTC architecture;

FIG. 4 is a flowchart illustrating a control method for a backoff timeraccording to an example of the present invention; and

FIG. 5 is a diagram showing the configuration of a preferred embodimentof a wireless device according to an example of the present invention.

BEST MODE

Mode for Invention

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toothers. Some components or characteristics of any embodiment may also beincluded in other embodiments, or may be replaced with those of theother embodiments as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

The embodiments of the present invention can be supported by thestandard documents disclosed in any one of wireless access systems, suchas an IEEE 802 system, a 3^(rd) Generation Partnership Project (3GPP)system, a 3GPP Long Term Evolution (LTE) and LTE-A system, and a 3GPP2system. That is, the steps or portions, which are not described in orderto make the technical spirit of the present invention clear, may besupported by the above documents. In addition, all the terms disclosedin the present document may be described by the above standarddocuments.

The following technologies may be used in various wireless communicationsystems. For clarity, 3GPP LTE and 3GPP LTE-A will be focused upon inthe following description, but the scope of the present invention is notlimited thereto.

Terms used in the present specification are as follows.

-   -   UMTS (universal mobile telecommunication system): Third        generation mobile communication technology based on global        system for mobile communication (GSM) developed by 3GPP.    -   EPS (evolved packet system): Network system including an evolved        packet core (EPC) which is a packet switched (PS) core network        based on internet protocol (IP) and an access network such as        LTE/UTRAN, which is evolved from UMTS.    -   NodeB: Base station of GERAN/UTRAN, which is mounted outdoors        and coverage of which forms a macro cell.    -   eNodeB: Base station of E-UTRAN, which is mounted outdoors and        coverage of which forms a macro cell.    -   UE: User equipment. The UE may be referred to as a terminal, a        mobile equipment (ME), a mobile station (MS), etc. In addition,        the UE may be a portable apparatus such as a laptop, a mobile        phone, a personal digital assistant (PDA), a smartphone and a        multimedia apparatus or a non-portable apparatus such as a        vehicle mounted apparatus. A UE or terminal may indicate an MTC        device in MTC.    -   Home NodeB (HNB): Base station of a UMTS network, which is        mounted indoors and coverage of which forms a micro cell.    -   Home eNodeB (HeNB): Base station of an EPS network, which is        mounted indoors and coverage of which forms a micro cell.    -   MME (mobility management entity): Network node of an EPS        network, which performs a mobility management (MM) function and        a session management (SM) function.    -   PDN-GW (packet data network-gateway)/PGW: Network node of an EPS        network, which performs a UE IP address allocation function, a        packet screening and filtering function and a charging data        collection function.    -   SGW (serving gateway): Network node of an EPS network, which        performs mobility anchor, packet routing, idle mode packet        buffering, triggering for enabling an MME to page a UE.    -   PCRF (policy and charging rule function): Network node of an EPS        network, which performs policy decision for dynamically applying        quality of service (QoS) and charging policy differentiated per        service flow.    -   OMA DM (open mobile alliance device management): Protocol        designed for management of mobile devices such as a mobile        phone, a PDA or a portable computer, which performs functions        such as device configuration, firmware upgrade, error report,        etc.    -   OAM (operation administration and maintenance): OAM is a set of        network administration functions for providing network fault        display, performance information, data and diagnostic functions.    -   NAS (non-access stratum): Upper stratum of a control plane        between a UE and an MME. This is a functional layer for        signaling between a UE and a core network and exchanging a        traffic message in an LTE/UMTS protocol stack, supports UE        mobility, and supports a session management procedure for        establishing and maintaining an IP connection between a UE and a        PDN GW.    -   NAS configuration MO (NAS configuration management object): MO        used to configure parameters associated with NAS functionality        with respect to a UE.    -   SIPTO (selected IP traffic offload): Scheme for transmitting        specific IP traffic through a public network such as the        Internet instead of an operator network when transmitting the        specific IP traffic through an H(e)NB or a macro cell. In a 3GPP        release-10 system, an operator selects a PDN-GW which is        physically close to a UE in an EPC network and supports handover        of user traffic.    -   PDN (packet data network): Network in which a server supporting        a specific service (e.g., a multimedia messaging service (MMS)        server, a wireless application protocol (WAP) server, etc.) is        located.    -   PDN connection: Logical connection between a UE and a PDN, which        is expressed by one IP address (one IPv4 address and/or one IPv6        prefix).    -   APN (Access Point Name): String indicating or identifying a PDN.        A requested service or a network (PDN) is accessed through a PGW        and the APN is the name (string) previously defined in the        network in order to find the PGW. For example, the APN may be        expressed by internet.mnc012.mcc345.gprs.    -   IMS (IP multimedia subsystem): Subsystem for providing a        multimedia service based on IP.    -   MTC (machine type communications): Communication performed by a        machine without human intervention.    -   MTC device: UE (e.g., a vending machine, a meter, etc.) which        has a communication function through a core network and serves a        specific purpose.    -   MTC-IWF (MTC interworking function): Entity serving as a gateway        for transmitting a control signal or data for MTC through a 3GPP        network including EPS or IMS.    -   SCS (service capability server): Server connected to a 3GPP        network for communication with an MTC device using an MTC-IWF        and an MTC device located in a home public land mobile network        (HPLMN). The SCS provides capability for utilizing one or a        plurality of applications.    -   MTC server: Server on a network for managing an MTC terminal,        which may be located inside or outside a mobile communication        network and may have an interface accessible by an MTC user. The        MTC server may provide an MTC associated service to other        servers (an SCS) and may be an MTC application server.    -   MTC application: Service to which MTC is applied (e.g., remote        metering, product movement tracking, etc.).    -   MTC application server: Server on a network in which an MTC        application is executed.    -   MTC feature: Function of a network supporting an MTC        application. For example, MTC monitoring is a feature for        preparing for equipment loss in an MTC application such as        remote metering and low mobility is a feature for an MTC        application for an MTC device such as a vending machine.    -   MTC subscriber: Entity which is connected to a network operator        and provides a service to one or more MTC terminals.    -   MTC group: Group of MTC terminals which share at least one MTC        feature and belong to an MTC subscriber.    -   RAN (radio access network): Unit including a NodeB, an eNodeB        and a radio network controller for controlling the NodeB and the        eNodeB in a 3GPP network, which is present between UEs and        provides connection to a core network.    -   HLR (home location register)/HSS (home subscriber server):        Database having subscriber information in a 3GPP network. The        HSS may perform functions such as configuration storage,        identity management and user state storage.    -   PLMN (public land mobile network): Network configured for the        purpose of providing a mobile communication service to        individuals. This network may be configured on a per operator        basis.    -   NAS level congestion control: Congestion or overload control        function of an EPS network composed of APN based congestion        control and general NAS level mobility management control.    -   MM back-off timer (mobility management back-off timer): Mobility        management back-off timer used to control congestion when        congestion occurs in a network. While the MM back-off timer        runs, a UE is set so as not to perform attach, location        information update (e.g., tracking area update (TAU)), routing        area update (RAU), service request/extended service request,        etc. (in case of an emergency bearer service, a paging response        in an existing region, or a multimedia priority service (MPS),        even when the MM back-off timer runs, the UE is set to make a        request).    -   SM back-off timer (session management back-off timer): Session        control back-off timer used to control congestion when        congestion occurs in a network. While the SM back-off timer        runs, a UE is set so as not to perform establishment or change        of a session based on an associated APN, etc. (in case of an        emergency bearer service or an MPS, even when the SM back-off        timer runs, the UE is set to make a request).    -   TA (tracking area): Registration area of a terminal in an EPS        network. The TA is identified by a tracking area identity (TAI).    -   RA (routing area): Registration area of a terminal for a packet        core network domain in a GPRS/UMTS network. The RA is identified        by a routing area identity (RAI).

Hereinafter, a description will be given based on the above-describedterms.

FIG. 1 is a diagram showing the schematic architecture of an evolvedpacket core (EPC).

The EPC is a fundamental element of system architecture evolution (SAE)for improving 3GPP performance. SAE corresponds to a research projectfor deciding a network structure supporting mobility between varioustypes of networks. SAE aims to provide an optimized packet-based systemwhich supports various radio access technologies based on IP andprovides improved data transfer capabilities.

More specifically, the EPC is a core network of an IP mobilecommunication system for a 3GPP LTE system and may support apacket-based real-time and non-real-time service. In the existing mobilecommunication system (that is, a second or third generation mobilecommunication system), a core network function was implemented throughtwo distinct sub-domains of a voice network (a circuit-switched (CS)network) and a data network (a packet-switched (PS) network). In a 3GPPLTE system which is evolved from the third generation communicationsystem, sub-domains of a CS network and a PS network were unified intoone IP domain. That is, in a 3GPP LTE system, a terminal having IPcapability and a terminal may be connected through an IP based basestation (e.g., an eNodeB (evolved Node B)), an EPC, an applicationdomain (e.g., an IMS)). That is, the EPC is a structure necessary toimplement an end-to-end IP service.

The EPC may include various components. FIG. 1 shows a serving gateway(SGW), a packet data network gateway (PDN GW), a mobility managemententity (MME), a serving GPRS (general packet radio service) (SGSN)supporting node and an enhanced packet data gateway (ePDG).

The SGW operates as a boundary point between a radio access network(RAN) and a core network and is an element which performs a function formaintaining a data path between an eNodeB and a PDG GW. In addition, ifa terminal moves over a region served by an eNodeB, the SGW serves as alocal mobility anchor point. That is, packets may be routed through theSGW for mobility in an evolved UMTS terrestrial radio access network(E-UTRAN) defined after 3GPP release-8 . In addition, the SGW may serveas an anchor point for mobility of another 3GPP network (an RAN definedbefore 3GPP release-8 , e.g., UTRAN or GERAN (global system for mobilecommunication (GSM)/enhanced data rates for global evolution (EDGE)radio access network).

The PDN GW corresponds to a termination point of a data interface for apacket data network. The PDN GW may support policy enforcement features,packet filtering and charging support. In addition, the PDN GW may serveas an anchor point for mobility management with a 3GPP network and anon-3GPP network (e.g., an untrusted network such as an interworkingwireless local area network (I-WLAN) and a trusted network such as acode division multiple access (CDMA) or WiMAX network).

Although the SGW and the PDN GW are configured as separate gateways inthe example of the network structure of FIG. 1, the two gateways may beimplemented according to a single gateway configuration option.

The MME performs signaling and control functions in order to supportaccess to network connection of a UE, network resource allocation,tracking, paging, roaming and handover. The MME controls control planefunctions associated with subscriber and session management. The MMEmanages numerous eNodeBs and signaling for selection of a conventionalgateway for handover to other 2G/3G networks. In addition, the MMEperforms security procedures, terminal-to-network session handling, idleterminal location management, etc.

The SGSN handles all packet data such as mobility management andauthentication of a user for other 3GPP networks (e.g., GPRS networks).

The ePDG serves as a security node for a non-3GPP network (e.g., anI-WLAN, a Wi-Fi hotspot, etc.).

As described with reference to FIG. 1, a terminal having IP capabilitiesmay access an IP service network (e.g., an IMS) provided by an operatorthrough various elements in the EPC based on 3GPP access or non-3GPPaccess.

FIG. 1 shows various reference points (e.g., S1-U, S1-MME, etc.). In the3GPP system, a conceptual link connecting two functions present indifferent functional entities of an E-UTRAN and an EPC is defined as areference point. Table 1 shows the reference points shown in FIG. 1. Inaddition to the example of Table 1 , various reference points may bepresent according to network structure.

TABLE 1 Reference point Description S1-MME Reference point for thecontrol plane protocol between E-UTRAN and MME S1-U Reference pointbetween E-UTRAN and Serving GW for the per bearer user plane tunnelingand inter eNodeB path switching during handover S3 Reference pointbetween MME and SGSN. Enables user and bearer information exchange forinter 3GPP access network mobility in idle and/or active state. Thisreference point can be used intra-PLMN or inter-PLMN (e.g. in the caseof Inter-PLMN HO). S4 Reference between SGW and SGSN. Provides relatedcontrol and mobility support between GPRS Core and the 3GPP Anchorfunction of Serving GW. In addition, if Direct Tunnel is notestablished, it provides user plane tunneling. S5 Reference point forproviding user plane tunneling and tunnel management between Serving GWand PDN GW. Used for Serving GW relocation due to UE mobility and if theServing GW needs to connect to a non-co-located PDN GW for the requiredPDN connectivity. S11 Reference point between MME and SGW SGi Referencepoint between the PDN GW and the packet data network. Packet datanetwork may be an operator external public or private packet datanetwork or an intra operator packet data network, e.g. for provision ofIMS services. This reference point corresponds to Gi for 3GPP accesses.

Among the reference points shown in FIG. 1, S2a and S2b correspond to anon-3GPP interface. S2a is a reference point for providing associatedcontrol between the trusted non-3GPP access and the PDNGW and mobilitysupport to a user plane. S2b is a reference point for providingassociated control between the ePDG and the PDNGW and mobility supportto a user plane.

FIG. 2 is a diagram showing examples of an MTC communication model.

Although communication through a PS network is defined in associationwith MTC in 3GPP GSM/UMTS/EPS, the present invention is not limited toMTC through the PS network and is applicable to MTC through the CSnetwork. In the current technical standard, a network structure isdefined using the existing bearer of a 3GPP system. Here, a method ofusing a short message service (SMS) for data exchange between an MTCdevice and an MTC server is proposed. Since a small amount of digitaldata such as metering information or product information is exchangeddue to the characteristics of an MTC application, an SMS is mostpreferably used and a conventional SMS method and an IMS based methodmay be supported. Methods of controlling a paging range for an MTCapplication with low mobility have been proposed.

The MTC application is executed in each of an MTC device and an MTCserver (e.g., an SCS) to interwork through communication using anetwork. At this time, various models of MTC traffic may be implementeddepending on what participates in communication between an MTCapplication and a 3GPP network. FIG. 2(a) shows a model in whichcommunication is directly performed without an MTC server (e.g., anSCS), FIG. 2(b) shows a model in which an MTC server (e.g., an SCS) islocated outside an operator domain, and FIG. 2(c) shows a model in whichan MTC server (e.g., an SCS) is located inside an operator domain. Inaddition, FIG. 2(a) corresponds to a direct communication schemecontrolled by a 3GPP operator, FIG. 2(b) corresponds to a communicationscheme controlled by a service provider, and FIG. 2(c) corresponds to acommunication scheme controlled by a 3GPP operator.

The direct model of FIG. 2(a) shows that an MTC application directlyperforms communication with a UE (or an MTC device) with respect to a3GPP network as an over-the-top (OTT) application.

The indirect model of FIGS. 2(b) and 2(c) shows that an MTC applicationindirectly performs communication with a UE (or an MTC device) using asupplementary service provided by a 3GPP network. More specifically, inthe example of FIG. 2(b), the MTC application may use an MTC server(e.g., an SCS) for supplementary services provided by a third-party(that is, for which 3GPP is not responsible) service provider. The MTCserver (e.g., the SCS) may perform communication with a 3GPP networkthrough various interfaces. In the example of FIG. 2(c), the MTCapplication may use an MTC server (e.g., an SCS) for supplementaryservices provided by a 3GPP operator (which corresponds to a serviceprovider). Communication between an MTC server (e.g., an SCS) and a 3GPPnetwork is performed within a PLMN. In FIGS. 2(b) and 2(c), an interfacebetween an MTC server (e.g., an SCS) and an MTC application is notincluded in the 3GPP standard.

Since the indirect models of FIGS. 2(a) and 2(b) are complementary, a3GPP operator may combine the indirect models for a differentapplication. That is, as shown in FIG. 2(d), an MTC communication modulemay be implemented as a hybrid model in which a direct model and anindirect model are simultaneously used. In case of the hybrid model, theMTC device may perform communication with a plurality of MTC servers(e.g., SCSs) in an HPLMN and an MTC server (e.g., an SCS) controlled bya service provider and an MTC server (e.g., an SCS) controlled by a 3GPPoperator may be different in terms of capabilities provided to an MTCapplication.

FIG. 3 is a diagram showing an exemplary model of an MTC architecture.

An end-to-end application between a UE (or an MTC device) used for MTCand an MTC application may use services provided by a 3GPP system andselective services provided by an MTC server (e.g., an SCS). A 3GPPsystem may provide transport and communication services (including a3GPP bearer service, and IMS and an SMS) including a variety ofoptimization services facilitating MTC. In FIG. 3, a UE used for MTC isconnected to a 3GPP network (UTRAN, E-UTRAN, GERAN, I-WLAN, etc.)through a Um/Uu/LTE-Uu interface. The architecture of FIG. 3 includesvarious MTC models described with reference to FIG. 2.

First, entities shown in FIG. 3 will be described.

In FIG. 3, an application server is a server on a network in which anMTC application is executed and may be referred to as an MTC applicationserver. Technologies for implementing various MTC applications areapplicable to an MTC application server and a detailed descriptionthereof will be omitted. In addition, the MTC application server mayaccess an MTC server (e.g., an SCS in FIG. 3) through a reference pointAPI and a detailed description thereof will be omitted. Alternatively,the MTC application server may be co-located with an MTC server (e.g.,an SCS).

AN MTC server (e.g., an SCS) is a server on a network for managing anMTC device and may be connected to a 3GPP network to communicate withnodes of a PLMN and a UE used for MTC.

An MTC-interworking function (IWF) may control interworking between anMTC server and an operator core network and serve as a proxy of MTCoperation. In order to support an MTC indirect or hybrid model, one ormore MTC-IWFs may be present in a home PLMN (HPLMN). The MTC-IWF mayrelay and interpret a signaling protocol on a reference point Tsp toenable a PLMN to perform a specific function. The MTC-IWF may perform afunction for authenticating an MTC server, a function for authenticatinga control plane request from an MTC server, various functions associatedwith the below-described trigger instructions, etc. before the MTCserver establishes communication with a 3GPP network.

A short message service-service center (SMS-SC)/Internet protocol shortmessage gateway (IP-SM-GW) may manage transmission and reception of anSMS. The SMS-SC serves to relay a short message between a short messageentity (SME) (an entity for transmitting or receiving a short message)and a mobile station and storing and forwarding the short message. TheIP-SM-GW may serve to perform protocol interworking between an IP basedUE and an SMS-SC.

A charging data function (CDF)/charging gateway function (CGF) mayperform a charging operation.

HLR/HSS serves to store and provide subscriber information (IMSI, etc.),routing information, configuration information, etc. to the MTC-IWF.

A mobile switching center (MSC)/SGSN/MME may perform a control functionsuch as mobility management, authentication, resource allocation, etc.for network connection of a UE. In association with the below-describedtriggering, the MSC/SGSN/MME may serve to receive a trigger instructionfrom the MTC-IWF and process the trigger instruction into the form of amessage provided to the MTC device.

A gateway GPRS support node (GGSN)/serving-gateway (S-GW)+packet datanetwork-gateway (P-GW) may serve as a gateway for connecting a corenetwork and an external network.

Table 2 shows main reference points of FIG. 3.

TABLE 2 Reference point Description Tsms Reference point used by anentity outside the 3GPP system to communicate with UEs used for MTC viaSMS. Tsp Reference point used by an SCS to communicate with the MTC-IWFrelated to control plane signaling. T4 Reference point used by MTC-IWFto route device trigger to the SMS-SC in the HPLMN. T5a Reference pointused between MTC-IWF and serving SGSN. T5b Reference point used betweenMTC-IWF and serving MME. T5c Reference point used between MTC-IWF andserving MSC. S6m Reference point used by MTC-IWF to interrrogate UEidentity (HSS/HLR for E.164 mobile station international subscriberdirectory number (MSISDN) or external identifier mapping to IMSI) andgather UE reachability and configuration information. S6n Referencepoint used by MTC-AAA to interrogate HSS/HLR.

Among T5a, T5b and T5c, one or more reference points may be referred toas T5.

In case of the indirect and hybrid model, user plane communication withan MTC server (e.g., an SCS) may be performed and, in case of the directand hybrid model, communication with an MTC application server may beperformed using a conventional protocol through Gi and SGi.

Details associated with description of FIGS. 2 to 3 may be incorporatedby referring to 3GPP TS 23.682.

NAS Level Congestion Control

In general, the case in which a network exceeds a limit of acontrollable communication amount may be referred to as a networkcongestion or overload state and operation for controlling atransmission/reception amount of a network to prevent network congestionmay be referred to as network congestion control. In a 3GPP MTC network,if network congestion or overload occurs, NAS level congestion controlis performed between a UE and a node (e.g., MME, SGW, PDN-GW, MSC, SGSNor GGSN) of a core network and thus signaling congestion may be avoidedor controlled.

Such NAS level congestion control includes AP based congestion controland general NAS level mobility management control.

APN based congestion control refers to signaling congestion controlaccording to a mobility management (MM)/session management (SM) protocolassociated with an APN (that is, an APN associated with a congestionstate) and a UE or an EPS mobility management (EMM)/EPS sessionmanagement (ESM) protocol. APN based congestion control includes APNbased session management congestion control and APN based mobilitymanagement congestion control.

General NAS level mobility management control means a code network node(e.g., MME, SGW, PDN-GW, MSC, SGSN or GGSN) rejects a mobilitymanagement signaling request made by a UE in a state of networkcongestion or overload to avoid congestion and overload.

In general, if a core network performs NAS level congestion control, areject message provided to a UE may include a standby time (or anextended standby time) value. Such a standby time value is randomizedwithin a predetermined range to be provided to the UE. The UE sets thereceived standby time value as a back-off timer value and operates so asnot to request (E)MM/(E)SM signaling from a network until the back-offtimer has expired.

(E)MM signaling includes, for example, an attach request, a TAU/RAUrequest, a service request, an extended service request, etc. Inaddition, (E)SM signaling includes, for example, PDN connectivity,bearer resource allocation, bearer modification, packet data protocol(PDP) context activation, PDP context modification request, etc. Theback-off timer may be divided into an MM back-off timer for control of(E)MM signaling and an SM back-off timer for control of (E)SM signaling.The MM back-off timer is assigned per UE and the SM back-off timer isassigned per associated APN or per UE. These timers may independentlyrun.

Additionally, in a 3GPP network, a terminal (e.g., an MTC device) may beconfigured through a NAS configuration MO to have “NAS signaling lowpriority”. The UE configured with the NAS signaling low priority setslow priority in a NAS message (e.g., an attach request, a TAU request, aPDN connection request, etc.) and transmits the NAS message.

In general, if a core network performs NAS level congestion control, aback-off timer (or an execution standby timer) value is included in areject message of a terminal configured with low priority (for example,if the NAS signaling low priority indicator is set such that a UE/MS isconfigured for NAS signaling low priority) to be transmitted. Asdescribed above, a terminal which receives a back-off timer value runsso as not to request (E)MM/(E)SM signaling from a network until aback-off timer (e.g., an MM back-off timer and/or an SM back-off timer)has expired.

Even when the back-off timer runs, an emergency service must beprovided. Accordingly, if a UE/MS has already performed or starts toperform an emergency bearer service with respect to service users havinga high priority, it is possible to make a request for the service evenwhen the MM/SM back-off timer runs. Service users having a high prioritymay access a network with multimedia priority service access classes 11to 15 , for example. Further, performing MT(Mobile Terminated) call/SMSservices and emergency call services are cases except for applyingback-off timer operations (i.e., those services may be provided eventhough the back-off timer is running).

Multiple Priorities

In a current 3GPP standard (Rel-10/Rel-11) MTC system environment, aUE/MS (hereinafter, referred to as a “terminal”) may be configured withonly one of two priorities, that is, “(NAS signaling) low priority” and“(NAS signaling) non-low priority”. For example, a NAS signaling lowpriority indicator may be set such that a UE/MS is configured for NASsignaling low priority or a UE/MS is not configured to NAS signaling lowpriority.

However, a terminal may have multiple priorities of two levels or moreaccording to future application environments. In addition, such multiplepriorities may be configured per device (or per terminal) or perapplication level. A priority configured per UE and a priorityconfigured per application may be separately (independently) configured.In addition, one of a plurality of priorities may be configured withrespect to one application.

Since operation associated with the priority in a conventional wirelesscommunication system is defined in consideration of only one of a “lowpriority” and a “non-low priority”, accurate operation may not beperformed if two or more priorities are configured. Accordingly, in thepresent invention, an operation method when multiple priorities areconfigured and an operation method when a priority is changed areproposed.

In order to configure different priorities per device or per applicationlevel to establish a PDN connection whenever a terminal having multiplepriorities establishes a PDN connection, it is necessary to compensatefor a method of establishing a PDN connection of a terminal havingmultiple priorities.

If a previously established PDN connection is a PDN connection having alow priority but a priority is newly changed to a different priority perdevice or per application level, the changed priority is applied to thenewly established PDN connection. In this case, how to process apreviously established PDN connection is ambiguous. For example, a PDNconnection method according to priority change should be provided inorder to determine whether a PDN connection having a previouslyconfigured priority is maintained or whether a PDN connection having apreviously configured priority is released and a newly changed priorityis applied to re-establish a PDN connection.

As described above, in a state in which an (E)MM back-off timer and an(E)SM back-off timer individually or simultaneously runs in a terminal,the terminal cannot request MM associated signaling and/or SM associatedsignaling from a network. However, if an emergency call/service or amultimedia priority service is used, the terminal may perform anassociated procedure even when the back-off timer runs.

How a terminal having multiple priorities per terminal or perapplication level performs operation based on an MM back-off timerand/or an SM back-off timer (hereinafter, referred to as a “MM/SMback-off timer”) if a priority is changed is ambiguous. For example, aback-off timer processing method according to priority change should beprovided in order to determine whether the existing MM/SM back-off timeris stopped or maintained if a priority is changed.

For example, since how a terminal having multiple priorities processes aPDN connection according to priority change or processes a running MM/SMback-off timer according to priority change due to network congestionwhen the MM/SM back-off timer runs is ambiguous, PDN connection controland/or NAS level congestion control cannot be accurately or efficientlyperformed. In this case, network state, service connectivity and userexperience are further deteriorated. Accordingly, if multiple prioritiesof two levels or more are applied and/or a priority is changed, there isa need for a new method of processing a PDN connection and an MM/SMback-off timer.

NAS Level Operation Improved by Applying Multipriority

As described above, it is assumed that MTC involves communicationbetween a large number of terminals and a network and the amount of dataof each terminal is relatively small and is not emergency data (e.g.,report of a metering result, etc.). Accordingly, an MTC device isgenerally configured for a low priority.

Examples of the present invention when two-level priority (or dualpriority) is applied will now be described. Here, dual priority, forexample, means that an NAS signaling low priority indicator may be setto “a UE/MS is configured for NAS signaling low priority” (hereinafter,referred to as “low priority”) or to “a UE/MS is not configured for NASsignaling low priority” (hereinafter, referred to as “not lowpriority”). However, the present invention is not restricted to dualpriority and may be applied to multipriority.

A conventional session management method considering a dual priorityfunction mainly handles a method for prohibiting SM related signaling(e.g., PDN connectivity, bearer resource allocation, bearermodification, PDP context activation, PDP context modification request,etc.) when an SM backoff is running for a specific APN.

Assume that a UE does not provide information about an APN during anattach procedure but an SM backoff timer is set because a network noderejects an NAS request of the UE. That is, the SM backoff timer is notset for a specific APN but may be set without an APN.

For example, an attach request message, on which information forrequesting a PDN connection without an APN is piggybacked, may be sent(this may be expressed as “an attach request without an APN istransmitted”). When a low-priority UE transmits an attach requestwithout an APN to a network node (e.g., MME), the network node mayconfigure an SM backoff timer for the UE if an APN, a PDN connectionwith the UE of which will be established, is congested (here, the UE hasmade a PDN request without an APN but the network node may specify anAPN for the PDN request (e.g., a default APN for the UE) based oninformation such as subscriber information). Here, the SM backoff timeris not configured for a specific APN but is configured without an APN.In this case, from the viewpoint of the UE, only the SM backoff timer isconfigured but an MM backoff timer is not configured. In this case,whether transmission of MM signaling (e.g., an attach request without anAPN) is permitted depending on whether the low priority indicator is setto “low priority” or “not low priority” is not clearly defined in therelated art.

More specifically, according to the related art, operation of a UE whenSM signaling (e.g., a PDN connectivity request, etc.) transmitted fromthe UE to a network is rejected due to “insufficient resources” and thusan SM backoff timer (e.g., T3396) information element (IE) is includedin a reject message is defined as follows.

-   -   When a PDN connectivity request is transmitted along with an        attach request, the UE performs the following different        operations according to integrity protection of an attach reject        message and a received value of the SM backoff timer.

If integrity protection of the attach reject message is not provided andthe SM backoff timer is running, the UE stops the SM backoff timer andthen starts the SM backoff timer using an arbitrary value in apredetermined range.

If integrity protection of the attach reject message is provided, the SMbackoff timer value is not 0 and is not deactivated and the SM backofftimer is running, the UE stops the SM backoff timer and then starts theSM backoff timer using a value provided by the SM backoff timer IE. Whenthe UE does not provide information about an APN during an attachprocedure, the UE is prohibited from starting a new attach procedurewithout an APN until the SM backoff timer has expired.

When the UE has transmitted an attach request without an APN to thenetwork but the attach request has rejected and thus the SM backofftimer is configured for the UE, the UE may not transmit a new attachrequest even when an MM backoff timer is not set. In this case, whethertransmission of a new attach request by a UE configured for dualpriority is permitted or prohibited according to “low priority” or “notlow priority” is not defined.

Overall system performance may deteriorate due to ambiguity of UEoperation in terms of configuration of a backoff timer for reducingnetwork congestion and important signaling transmission.

The embodiments of the present invention for solving this problem willnow be described.

First, a method of handling low priority indication for NAS signalingwill be described.

A UE may include an information element (IE) such as device propertiesin an NAS message and set a low priority indicator to “the UE isconfigured for NAS signaling low priority”, thereby indicating that theUE is configured for low priority. The UE sets the low priorityindicator to “not low priority” in the following cases:

-   -   the UE is performing attach for an emergency bearer service;    -   the UE has a PDN connection for establishment of an emergency        bearer service and is performing an EPS MM procedure or is        establishing a PDN connection for an emergency bearer service;    -   the UE configured for dual priority is requested by an upper        layer to establish a PDN connection having low priority        indicator set to not low priority;    -   the UE configured for dual priority is performing an EPS session        management (SM) procedure related to the PDN connection        established with the low priority indicator set to “not low        priority”;    -   the UE configured for dual priority has a PDN connection        established by setting the low priority indicator to “not low        priority” and is performing EPS mobility management (MM)        procedure;    -   the UE is accessing the network with access classes 11 to 15; or    -   the UE is responding to paging.

The network may use NAS signaling low priority indication, for NAS levelMM congestion control and APN based congestion control.

When the NAS signaling low priority indication is included in a PDNconnectivity request message, the MME stores the NAS signaling lowpriority indication in a default EPS bearer context activated by the PDNconnectivity request procedure.

Next, a method of handling an SM request to a UE configured for dualpriority will be described.

First, prior to operation of the UE when an SM backoff timer without anAPN is configured according to the present invention, configuration ofan SM backoff timer for a specific APN will be described.

If the SM backoff timer (e.g., T3396) is running for the specific APN,because a PDN connection request, bearer resource modification requestor bearer resource allocation request message including a low priorityindicator set to low priority was rejected due to “insufficientresources”, when the SM backoff timer is configured, according to therequest of the upper layer, the UE may:

-   -   send a PDN connectivity request message to the same APM, with        the low priority indicator set to “not low priority”; or    -   if a PDN connection established with the low priority indicator        set to “not low priority” exists, send the bearer resource        modification request or bearer resource allocation request        message for this PDN connection. At this time, the low priority        indicator is set to “not low priority”.

According to proposals of the present invention when the SM backofftimer without an APN is configured, the UE operates as follows.

If the SM backoff timer is running without an APN, because the PDNconnectivity request message transmitted along with the attach requestmessage including the low priority indicator set to the low priority wasrejected due to “insufficient resources”, when the SM backoff timer isconfigured, the UE may initiate a new attach procedure without an APN,with the low priority indicator set to “not low priority”, according tothe request of the upper layer.

That is, when the SM backoff timer is configured because the PDNconnectivity request transmitted along with the attach request withoutan APN was rejected, the new attach request message (that is, the attachrequest message without an APN) may not be transmitted if “low priority”is set and may be transmitted if “not low priority” is set.

When the SM backoff timer is running, transmission of the attach requestwithout an APN, which is set to a low priority, may be prohibited toprevent network congestion from increasing and transmission of the newattach request, which is set to “not low priority”, is permitted toprotect emergency/important signaling, thereby clarifying UE operationand improving overall system performance. For example, it is possible toprevent unnecessary service delay/communication delay between the UE andthe network and to prevent network resources from being unnecessarilywasted.

Similarly, the proposal of the present invention is applicable to an SMrequest related to a “PDP context activation request”.

First, prior to operation of the UE when the SM backoff timer without anAPN is configured, configuration of the SM backoff timer for a specificAPN will be described.

If the SM backoff timer is running for the specific APN, because a PDPcontext activation request, secondary PDP context activation request orPDP context request modification message including a low priorityindicator set to low priority was rejected due to “insufficientresources”, when the SM backoff timer is configured, according to arequest of an upper layer, the UE may:

-   -   send a PDP context activation request message to the same APN,        with the low priority indicator set to “not low priority”; or    -   if a PDN connection established with the low priority indicator        set to “not low priority” exists, send the secondary PDP context        activation request or PDP context modification request message        for this PDN context. At this time, the low priority indicator        is set to “not low priority”.

According to the proposal of the present invention when the SM backofftimer without an APN is configured, the UE operates as follows.

If the SM backoff timer without an APN is running, because the PDPcontext activation request message including the low priority indicatorset to the low priority was rejected due to “insufficient resources”,when the SM backoff timer is configured, the UE may transmit the PDPcontext activation request message without an APN, with the low priorityindicator set to “not low priority”, according to the request of theupper layer.

That is, when the SM backoff timer is configured because the PDP contextactivation request without an APN was rejected, the new PDP contextactivation request (that is, the PDP context activation request messagewithout an APN) may not be transmitted if “low priority” is set and maybe transmitted if “not low priority” is set.

When the SM backoff timer is running, transmission of the PDP contextactivation request, which is set to the low priority, may be prohibitedto prevent network congestion from increasing and transmission of thenew PDP context activation request without an APN, which is set to “notlow priority”, is permitted to protect emergency/important signaling,thereby clarifying UE operation and improving overall systemperformance. For example, it is possible to prevent unnecessary servicedelay/communication delay between the UE and the network and to preventnetwork resources from being unnecessarily wasted.

Additionally, if the UE has multi-level priority of three levels ormore, the MM backoff timer and/or the SM backoff timer may be appliedaccording to the priority level. In the case of priority to which theMM/SM backoff time (e.g., one or more low priorities of multi-levelpriorities) is applied, when the PDN connectivity request message istransmitted alone, when the attach request message is transmitted alongwith the PDN connectivity request or when the PDP context activationrequest message is transmitted, congestion control is performed by theMM/SM backoff timer. For example, the NAS request may not be made whilethe backoff timer is running.

In the case of priority to which the MM/SM backoff timer is not applied(e.g., one or more high priorities of multi-level priorities), when thePDN connectivity request message is transmitted alone, when the attachrequest message is transmitted along with the PDN connectivity requestor when the PDP context activation request message is transmitted,congestion control is not performed by the MM/SM backoff timer. Forexample, the NAS request may be made even when the backoff timer isrunning.

FIG. 4 is a flowchart illustrating a control method for a backoff timeraccording to an example of the present invention.

In step S410, the UE may transmit an NAS request without an APN (e.g.,an attach request without an APN), which is set to a first prioritylevel (e.g., a low priority level), to the network.

In step S420, if the network is congested (or resources areinsufficient), the UE may receive a reject message for the NAS requestfrom the network. Here, the reject message may include the SM backoffinformation.

In step S430, the UE may initiate the SM backoff timer.

In step S440, when the UE attempts to transmit a new NAS request(initiates a new attach procedure) while the SM backoff timer isrunning, whether the new NAS request is set to a first priority may bedetermined.

If the result of step S440 is yes (that is, the new NAS request is setto the first priority (or low priority)), the method progresses to stepS450, in which the UE does not permit transmission of the new NASrequest while the SM backoff timer is running.

If the result of step S440 is no (that is, the new NAS request is notset to the first priority (or low priority), the method progresses tostep S460, in which the UE permits transmission of the new NAS requestwhile the SM backoff timer is running.

In the backoff timer control method of the present invention describedwith reference to FIG. 4, the above-described embodiments of the presentinvention may be independently applied or two or more of theabove-described embodiments may be simultaneously applied.

In addition, although the above-described examples of the presentinvention are applied to a wireless communication service of an MTCmethod, the principle of the present invention is equally applicable tooperation according to multipriority in a general wireless communicationsystem, control operation of a backoff timer, etc.

According to the above-described embodiments of the present invention,it is possible to prevent unnecessary delay in a service/communicationbetween a UE and a network, to prevent network resources from beingunnecessarily wasted, and to improve user experience.

FIG. 5 is a diagram showing the configuration of a preferred embodimentof a wireless device according to an example of the present invention.

Referring to FIG. 5, the wireless device according to the presentinvention may include a transceiving module 1010, a processor 1020 and amemory 1030. The transceiving module 101 may be configured to transmitvarious signals, data and information to an external device (e.g., anetwork node, a terminal, a server, etc.) and receive various signals,data and information from an external device (e.g., a network node, aterminal, a server, etc.). The processor 1020 may control overalloperation of the wireless device and the wireless device may beconfigured to perform a function for processing information transmittedor received to or from an external device. The memory 1030 may store theprocessed information for a predetermined time and may be replaced by abuffer (not shown).

The wireless device according to the embodiment of the present inventionmay be configured to control the backoff timer if multipriority is set.The processor 1020 may be configured to transmit an NAS request messagewithout an APN (e.g., an attach request message without an APN), whichis set to the first priority level (e.g., a low priority), to thenetwork node using the transceiving module 1010. In addition, theprocessor 1020 may be configured to receive the reject message for theNAS request message from the network node using the transceiving module1010. The processor 1020 may be configured to initiate the SM backofftimer based on the reject message. In addition, the processor 1020 maybe configured to permit transmission of a new NAS request message whichis not set to the first priority level (or is not set to a low priority)while the SM backoff timer is running. The processor 1020 may beconfigured to prohibit transmission of the new NAS request message whichis set to the first priority level (or is set to the low priority) whilethe SM backoff timer is running.

The embodiments of the present invention may be independently orsimultaneously applied to the detailed configuration of the wirelessdevice and a description thereof will be omitted for clarity.

The embodiments of the present invention can be implemented by a varietyof means, for example, hardware, firmware, software, or a combinationthereof.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. Software code may be stored in a memory unit so that itcan be driven by a processor. The memory unit is located inside oroutside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other. Accordingly, the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predeterminedmanner. Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with other claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The above-described embodiments of the present invention are applicableto various mobile communication systems.

What is claimed is:
 1. A method of controlling a backoff timer at a userequipment (UE) configured for multipriority, the method comprising:transmitting a first non access stratum (NAS) request message without anaccess point name (APN), which is set to a first priority level, to anetwork node, wherein the first NAS request message without the APN isan attach request message transmitted along with a packet data network(PDN) connectivity request without an APN; receiving a reject messagefor the first NAS request message from the network node; initiating asession management (SM) backoff timer based on the reject message; andtransmitting a second NAS request message, which is not set to the firstpriority level, while the SM backoff timer is running.
 2. The methodaccording to claim 1, wherein the UE does not provide the APN during aprocedure initiated by transmitting the first NAS request messagewithout the APN.
 3. The method according to claim 2, wherein theprocedure initiated by transmitting the first NAS request messagewithout the APN is an attach procedure.
 4. The method according to claim1, wherein the reject message includes a value for the SM backoff timerwhich is running while the second NAS request message is transmitted. 5.The method according to claim 1, wherein a clause in the reject messageis set to insufficient resources.
 6. The method according to claim 1,wherein the UE configured for multipriority is a UE configured for dualpriority.
 7. The method according to claim 6, wherein the first prioritylevel corresponds to the UE being configured for NAS signaling lowpriority.
 8. The method according to claim 6, wherein the first prioritylevel corresponds to a low priority indicator, which is set to the UEbeing configured for NAS signaling low priority.
 9. The method accordingto claim 1, wherein the UE is a machine type communication (MTC) device.10. A user equipment (UE) device for controlling a backoff timer ifmultipriority is set, the UE comprising: a transceiver module; and aprocessor, wherein the processor configured to: transmit a first nonaccess stratum (NAS) request message without an access point name (APN),which is set to a first priority level, to a network node using thetransceiver module, wherein the first NAS request message without theAPN is an attach request message transmitted along with a packet datanetwork (PDN) connectivity request without an APN, receive a rejectmessage for the first NAS request message from the network node usingthe transceiver module, initiate a session management (SM) backoff timerbased on the reject message, and transmit a second NAS request message,which is not set to the first priority level, while the SM backoff timeris running.